The Ebola virus has been found in semen up to 82 days after the onset of symptoms, the World Health Organization says in advising men who’ve recovered from the virus to abstain from sex for three months.

Ebola is spread through direct contact with an infected person’s blood, including urine, saliva, sweat, feces, vomit, breast milk and semen, says the U.S. Centers for Disease Control and Prevention (CDC).

“Men who have recovered from Ebola virus disease should be aware that seminal fluid may be infectious for as long as three months after onset of symptoms,” the World Health Organization said in a statement released Friday.

“Because of the potential to transmit the virus sexually during this time, they should maintain good personal hygiene after masturbation, and either abstain from sex (including oral sex) for three months after onset of symptoms, or use condoms if abstinence is not possible.”

Although the WHO’s statement focused on men, previous reports also show that that Ebola DNA can stay present in the vaginal secretions of female survivors for at least several weeks after they recover.

‘Disturbing trend’ of possibly sexually transmitted Ebola infections

While sexual transmission of Ebola virus disease has not been officially documented, local health officials have expressed concerns in recent days that men are transmitting the virus to their partners after being released from treatment.

Dr. Atai Omurutu, the head of Liberia’s largest treatment center, told news agency All Africa that he has witnessed a “disturbing trend” in the country’s clinics: “Almost all the wives of male Ebola survivors are coming to the [Ebola clinics] as patients,” he said.

Dr. Omurutu appealed to Liberian President Ellen Johnson Sirleaf, who toured the country’s treatment units this week, to work with the Ministry of Health to set up free condom distribution programs at the clinics.

Although it is unknown whether Ebola can be spread through semen, scientists have previously documented sexual transmission of the closely-related Marburg virus, and an article in the Wall Street Journal this month presents anecdotal evidence of Ebola infection via sexual contact.

The article tells the story of Helena Henry, an Ebola survivor in Liberia. Ebola swept through her family, killing her grandmother, two brothers, and a sister in law. When she and her mother became ill, they went to a clinic outside the capital of Monrovia where she recovered and her mother died.

After being released, she went home to her partner of 12 years and the two had sex. He became ill a week later, and two weeks after that he died. There is no way to know whether he got the virus through sexual intercourse, but Henry suspects he did.

Sexual transmission of Ebola could reignite outbreak

Ebola, like other viruses, is present in all bodily fluids: blood, vomit, feces, sweat, saliva, tears, urine, semen, and vaginal fluids. Those most at risk of contracting Ebola are the people who come in direct contact with a severely ill patient because the symptoms of the virus include vomiting, diarrhea, and unexplained bleeding.

Laboratory studies show that the virus is usually detectable at very low levels in a patient’s blood once they begin experiencing fever and increases logarithmically during the acute phase of infection. The bodies of people who die from Ebola are particularly infectious.

For those who survive, the level of virus in their blood drops during their clinical recovery. Few survivors have been studied in lab settings, but the longest that any study has found detectable levels of the virus in a survivor’s blood is 21 days after the onset of symptoms.

The same is not true of semen, however. Studies have found the virus in semen as many as 101 days after symptom onset and in vaginal fluid up to 33 days after symptoms began.

With up to 45 percent of male Ebola patients surviving the disease, experts are concerned that transmission through sexual activity could reignite the epidemic. The WHO has warned that sexual transmission could even bring the virus back to places like Senegal and Nigeria, which appear free of the disease.

More than 15, 935 cases of Ebola have been reported since the outbreak began in March. Almost all the cases and deaths have been in Guinea, Sierra Leone and Liberia — the three hardest-hit countries, which reported more than 600 new cases in the past week, the WHO said in its latest update.